The present invention relates to multi-cylinder internal combustion engines of the type including:
at least one intake valve and at least one exhaust valve for each cylinder, each provided with respective biassing spring means which bias the valve towards a closed position, for controlling respective intake and exhaust conduits,
at least one camshaft, for operating the intake valves and the exhaust valves of the cylinders of the engine, through respective tappets,
in which at least each intake valve has a variable actuation, by being controlled by the respective tappet, against the action of said biasing spring means, through the interposition of hydraulic means including a chamber of fluid under pressure, facing a pumping piston connected to the valve tappet,
said chamber of fluid under pressure being adapted to be connected through a solenoid valve to a discharge channel, in order to uncouple the variable actuation valve from its respective tappet and to cause the rapid closure of the valve under the action of its respective biasing spring means, and
electronic control means for controlling each solenoid valve so as to vary the time and extension of the opening of the variable actuation valve as a function of one or more operating parameters of the engine.
The Applicant has been developing electronically-controlled hydraulic devices of the type specified above, for the variable actuation of engine valves since long. The Applicant also owns various patents and patent applications relating to engines provided with systems of this type. For prompt reference, FIG. 1 of the attached drawings shows in cross-section an engine according to this technology, as described in European patent EP 0 803 642 B1 belonging to the Applicant.
With reference to FIG. 1, the engine shown therein is a multi-cylinder engine, for example an engine with four cylinders in line, including a cylinder head 1.
The head 1 comprises, for each cylinder, a cavity 2 formed on the base surface 3 of the head 1, defining the combustion chamber, into which two intake conduits 4, 5 and two exhaust conduits open. Communication of the two intake conduits 4, 5 with the combustion chamber 2 is controlled by two intake valves 7, of the conventional mushroom-shaped type, each comprising a stem 8 slidably mounted in the body of the head 1.
Each valve 7 is biassed towards the closed position by springs 9 interposed between an inner surface of the head 1 and a valve cup 10. Communication of the two exhaust conduits 6 with the combustion chamber 2 is controlled by two valves 70, again of the conventional type, to which there are associated springs 9 to bias them towards the closed position.
Opening of each intake valve 7 is controlled, in a manner that will be described below, by a camshaft 11 rotatably mounted around an axis 12 within supports of the head 1, and comprising a plurality of cams 14 to operate the intake valves 7.
Each cam 14 that controls an intake valve 7 cooperates with the plate 15 of a tappet 16 slidably mounted along an axis 17 that, in the case of the example illustrated in the document cited above, is directed substantially at 90° with regard to the axis of the valve 7. The plate 15 is biassed against the cam 14 by a spring associated thereto. The tappet 16 comprises a pumping piston 16 slidably mounted within a bush 18 carried by a body 19 of a pre-assembled unit 20, incorporating all the electric and hydraulic devices associated with the operation of the intake valves, according to what will be described in detail below.
The pumping piston 16 is capable of transmitting a force to the stem of the valve 7, in such a manner as to cause the opening of the latter against the action of the spring means 9, through fluid under pressure (preferably oil from the engine lubrification circuit) present in a pressure chamber C which faces the pumping piston 16, and through a piston 21 slidably mounted in a cylindrical body comprising a bush 22 that is likewise carried by the body 19 of the sub-unit 20.
In the known solution illustrated in FIG. 1, the chamber of fluid under pressure C associated to each intake valve 7 may be placed in communication with a discharge channel 23 through a solenoid valve 24. The solenoid valve 24, which may be of any known type appropriate to the function illustrated here, is controlled by electronic control means, diagrammatically illustrated and designated by 25, depending upon signals S indicative of the operating parameters of the engine, such as the position of the accelerator and the number of revolutions of the engine.
When the solenoid valve 24 is open, the chamber C enters into communication with the channel 23, so that the fluid under pressure present in the chamber C flows into that channel and the cam 14 and respective tappet 16 are uncoupled from the intake valve 7, which thus rapidly returns to its closed position under the action of the biasing spring 9. By controlling communication between the chamber C and the discharge channel 23, it is therefore possible to vary at will the time and extension (lift) of the opening of each intake valve 7.
The discharge channels 23 of the various solenoid valves 24 all lead into the same longitudinal channel 26 communicating with pressure accumulators 27, only one of which is shown in FIG. 1.
All the tappets 16 with the associated bushes 19, 18, the piston 21 with the associated bushes 22, the solenoid valves 24 and the relative channels 23, 26 are carried by or formed in said body 19 of the pre-assembled unit 20, to advantage in terms of the speed and simplicity of assembling the engine.
The exhaust valves 70 associated with each cylinder are controlled, in the embodiment shown in FIG. 1, in the traditional manner, by a respective camshaft 28, through respective tappets 29, although in principle, in the case of the document identified above, an application of the hydraulic operating system also to the control of the exhaust valves is not excluded.
Again with reference to FIG. 1, the variable-volume chamber defined inside bush 22 and facing piston 21 (which in FIG. 1 is shown in its minimum volume condition, the piston 21 being in its upper end-of-stroke position) communicates with the chamber of fluid under pressure C through an opening 30 formed in one end wall of bush 22. This opening 30 is engaged by an end prong 31 of the piston 21 in such a manner as to achieve a hydraulic braking action of the movement of the valve 7 in the closing phase, when the valve is close to the closed position, since the oil present in the variable-volume chamber is forced to flow into the chamber of fluid under pressure C passing through the play existing between the end prong 31 and the wall of the opening 30 engaged by it. As well as the communication constituted by the opening 30, the chamber of fluid under pressure C and the variable-volume chamber of the piston 21 communicate with each other through inner passages obtained one-way valve 32 that enables passage of the fluid only from the chamber under pressure C to the variable-volume chamber of the piston 21.
During normal operation of the known engine illustrated in FIG. 1, when the solenoid valve 24 excludes communication of the chamber of fluid under pressure C with the discharge channel 23, the oil present in said chamber transmits movement of the pumping piston 16, imparted by the cam 14, to the piston 21 that controls opening of the valve 7. In the initial phase of the opening movement of the valve, the fluid coming from the chamber C reaches the variable-volume chamber of the piston 21 passing through the one-way valve 32 and further passages that place the inner cavity of the piston 21, which has a tubular shape, in communication with the variable-volume chamber. After a first displacement of the piston 21, the prong 31 leaves the opening 30, so that the fluid coming from the chamber C can pass directly into the variable-volume chamber through the opening 30, now free.
In the opposite movement of valve closing, as was said above, during the final phase the prong 31 enters the opening 30 causing hydraulic braking of the valve, so as to avoid collision of the body of the valve against its seat, for example subsequent to an opening of the solenoid valve 24 that causes the immediate return of the valve 7 to the closed position.
As an alternative to the hydraulic braking device shown in FIG. 1, the Applicant has already also proposed (see European patent application EP 1 344 900 A2) a different solution in which the piston 21 controlling the intake valve of the engine is without an end prong and the one-way valve 32 instead of being located in the body of the piston 21 is located in a fixed part. Furthermore, one or more passages communicating directly with the pressure chamber C have their outlets in the wall of the bush within which the piston 21 is mounted in a sliding manner. These passages are shaped and positioned in such a manner that they are progressively intercepted by the piston 21 in the final phase of closure of the engine valve, in order to cause a restriction of the section of fluid passage, with a consequent hydraulic braking effect. Furthermore, in the solution proposed in application for European patent EP 1 344 900 A2, an auxiliary hydraulic tappet is situated between the piston 21 that controls the engine valve and the stem of the engine valve.
In order to illustrate another significant example of application, already proposed by the same Applicant, FIG. 2 of the attached drawings shows the embodiment forming the subject of the prior application for a European patent EP 1 653 057 A1 by the same Applicant. In this case the engine is provided with a single camshaft to control both the intake valves and the exhaust valves.
With reference to FIG. 2, all the members of the electronically-controlled hydraulic device are carried by a single “brick” structure 200 that has a lower plane that, in the assembled condition, corresponds to the plane passing through the axes of two shafts 11, 28. The shaft 11 is the sole camshaft of the engine and is thus provided both with cams to control the intake valves and with cams to control the exhaust valves of the engine, whereas the shaft 28 is a shaft without cams having one extremity coming out of the cylinder head bearing a power takeoff that can be exploited to operate any auxiliary system.
Similarly to a conventional engine, the two shafts 11, 28 have extremities likewise external to the cylinder head bearing gears 202, 203 which are to engage with the gearing chain that transmits motion from the driving shaft to the shafts 11, 28.
The shaft 11, as discussed above, is provided with both cams operating the engine intake valves and cams operating the exhaust valves. According to a solution already proposed in EP 1 555 398 A1 by the same Applicant, the cams controlling the intake valves control them through an electronically-controlled hydraulic device of a type similar to that described with reference to FIG. 1. In FIG. 2, the parts of said device are indicated with the same reference numbers used in FIG. 1. Vice versa, the exhaust valves are operated mechanically by the respective cams of the shaft 11. As is clear in FIG. 2, the exhaust valves are operated by rocker arms 204, each of which has one extremity 205 pivoted to the cylinder head structure, an intermediate roller making contact with the respective cam, and the opposite extremity 206 that operates the respective exhaust valve 70. The pumping element 16 associated to each intake valve is, on the contrary, controlled by a rocker arm 207 pivoted to the “brick” structure 200 and that has portions engaging respectively with the controlling cam carried by the shaft 11, and with the pumping element 16. FIG. 2 also shows the sparking plug 208 (and the relative coil 209) associated to the cylinder of the engine. As has been said, the “brick” bears all the elements making up the electronically-controlled hydraulic device for the variable operation of the intake valve 7, as well as all the ducts of the hydraulic system associated to that device.